Completion system for secondary recovery



Nov. 2, 1965 o. M. KIEL COMPLETION SYSTEM FOR SECONDARY RECOVERY s sheets-sheet 1- Filed D60. l, 1960 2 AIU. P

FIG. l

lnvenior Orhor M. Kiel Nov. 2, 1965 o. M. KIEL 3,215,197

COMPLETION SYSTEM FOR SECONDARY RECOVERY Filed Dec. 1, 1960 5 Sheets-Sheet 2 l l l l n l l I l l I I 4 l l a I l Other M. Kiel Inventor Byv MAHornev Nov. 2, 1965 o. M. KIEL COMPLETION SYSTEM FOR SECONDARY RECOVERY 5 Sheets-Sheet 3 Filed Deo. l, 1960 I.OO

WATER sATuRATldN FIG.

Inventor Othor M. Kiel United States Patent O 3,215,197 COMPLETION SYSTEM FOR SECONDARY RECOVERY Othar M. Kiel, Tulsa, Okla., assignor, by mesne assignments, to Esso Production Research Company, Houston, Tex., a corporation of Delaware Filed Dec. 1, 1960, Ser. No. 73,045 3 Claims. (Cl. 166-9) This invention is related to the completion of Wells drilled into a subterranean formation. More specifically the invention is concerned with the completion of wells in a secondary recovery operation in which separate channels are established within the well from the surface to within the formation.

It is well known that petroleum is commonly produced from underground or subterranean formations in which the petroleum has been trapped. This is normally accomplished by drilling a borehole from the surface into the producing horizon and permitting the fluid to ow into the Well bore and thence be removed to the surface. It is equally well known that the energy which forces the petroleum from the formation to the Well bore is dissipated, during displacement of the oil, and there usually remains, when this energy is expended, one-half to as much as two-thirds or more of the original oil in place that is still unproduced. In an attempt to regain additional oil from such a reservoir so-called secondary operations are instituted. In these operations, it is common practice to inject a iiuid through one well that has been drilled into the producing formation to force oil through the formation and into another well commonly termed a production well whereby the oil may be recovered.

In early secondary recovery projects, it was customary to inject a single fluid such as air or more frequently water through the input Well to drive the unproduced oil toward the production well. More recently, techniques have been developed wherein two or more fluids are injected to obtain greater recoveries. One such recently developed technique is the simultaneous injection of a mixture of two immiscible fluids such as water and a liquitied petroleum gas (LPG) such as propane or butane, for example. An undesirable feature of such a mixture is that the constituents normally have different specific gravities. To obtain maximum effectiveness of the injection of water and propane it is desired that they enter the formation simultaneously in a mixed condition. Heretofore this has been most ditiicult to do. The water and LPG may be mixed at the surface but as is known the two substances are not miscible and have different specific gravities. Due to gravity segregation occurring, the LGG fand the Water become separated with the result that the water enters the lower part of the formation and the LPG enters the uper portion of the formation. It is thus seen that there is a need wherein two iiuids such as water and LPG can be injected simultaneously into an underground reservoir without gravity segregation occurring. This invention provides a solution to that problem.

Briefly, this invention pertains to a secondary recovery system wherein two fluids having different specific gravities are injected as a driving mechanism through an input 'Well penetrating the subterranean formation. In the practice of the invention, two separate channels are established within the Well from the surface to Within the forice mation. One iiuid is injected through one of the channels and the second fluid through the other.

In a preferred embodiment two tubular members are suspended in a well bore from the surface to the formation. The void within the well, exterior to the two tubular members, is filled with cement at least opposite the formation. Thereafter each tubular formation is perforated through the vertical section which is to be under the process. The perforations of each tubular member do not have direct access to one another. In the situation given above, for example, LPG is injected through all the perforations in one tubular member. This assures vertical distribution of the LPG. Through the second tubular member, water is injected through the perforations directly into the formation. This assures vertical distribution of the water. The fluids are then injected in a manner so that they are distributed vertically as desired in the formation. Once these fluids have entered the formation there is very little tendency for gravity segregation to occur because most formations have a much greater horizontal permeability than vertical permeability.

The objects and a better understanding of this invention can be had from the following description taken into conjunction with the drawing in which:

FIG. 1 illustrates a cross-sectional view of a well completed in accordance with this invention;

FIG. 2 is a section view taken across the line 2--2 of FIG. 1;

FIG. 3 is another embodiment of a Well completion in a multi-zone reservoir;

FIG. 4 is a section view taken along the line 4-4 of FIG. 3;

F FIG. 5 is a section view taken along the line 5 5 of FIG. 6 is a section view taken along the line 6 6 of FIG. 3; and

FIG. 7 shows curves illustrating the relative permeability of the formation to oil and water for various water saturations.

Turning now to the drawing and FIG. 1 in particular, there is illustrated a well bore 10 in which has been suspended a rst tubular member 12 and a second tubular member 14. The well bore 10 is illustrated as penetrating through a pressure depleted oil reservoir 16. The two tubings 12 and 14 are positioned in the well bore in any well known manner and extend to the surface where they connect with conventional well equipment not shown. The void within the well bore, exterior of tubular members 12 and 14, is filled with a cement 18 in a known manner. Conventional cement used in setting the casing and the like is quite adequate for this purpose.

After the cement has set, each tubing is perforated independently. Tubing 12 has vertically spaced perforations 20 and tubular member 14 has vertically spaced perforations 22. As shown in FIG. 2 the tubular members 12 and 14 are spaced diametrically opposite each other on a diameter across the well bore 10. Tubing 12 is shown as perforated in one direction and tubular member 14 in the opposite direction. These perforations can be performed by commercially available and directional perforating systems. As an example, water is injected through tubing member 14 and LPG is injected through tubing member 12. It is, of course, apparent that if more than two fluids of different gravities and different miscibilities are desired for simultaneous injection, an additional string of tubing may be used as necessary.

Turning now to FIG. 3 and sectional views thereof of FIG. 4, FIG. 5 and FIG. 6, there is illustrated a system of multiple strings of tubing for injecting simultaneously two fluids such as LPG and water into various zones or formations spaced vertically in the borehole. Illustrated in FIG. 3 are borehole 24 extending through three vertically spaced producing formations 26, 28 and 30. Upper zone 26 and middle zone 28 are separated by impermeable barrier 32 and the lower producing Zone is separated from the middle producing zone 28 by impermeable barrier 34. Spaced from each other and suspended from the surface are tubular members 36 and 38 which extend through the oil producing interval 30; tubings 40 and 42 which extend through middle producing zone 28; and tubings 44 and 46 which extend through upper zone 26.

The void in the well bore, exterior of the tubular members, is lled with a cementing material 48. The cement is placed therein in a manner well known to those skilled in the art such that the tubings are essentially free of the cement. This can conveniently be done by having all the lower ends of the tubing closed except one. The tubing with the open end is used to pump cement to the bottom of the well bore and into the void. After the tubing strings have been set, they are then directionally perforated. Tubings 36 and 38 are perforated through the vertical interval of the producing zone 30 with perforations and 52. Likewise the tubings 40 and 42 are perforated to have perforations 54 and 56 extending vertically through formation 28. Tubings 44 and 46 have perforations 58 and 60 extending respectively vertically into formation 26. It is preferred that the vertical patterns of perforations for each pair of tubing such as 36 and 38 be similar. This assures that each segment of the section receives its proportional share of the injected fluids.

It is thus believed quite clear that the fluids injected into the formation through the dilferent tubing strings such as 36 and 38 are injected in a desired vertical pattern. Further, the uids injected through tubings 36 and 38 communicate only after they are in the formation. The fluids injected through tubing 36 and through tubing 38 can be considered as being injected at a point when the size of the well bore is compared to the size of the area of the reservoir. The fluids injected into the reservoir through perfor-ations 52 and perforations 50, for example, will communicate in the reservoir at the same pro-- portion as they emerge from perforations 50 and 52. If a proper ratio for the LPG and the water is maintained each of the constituents will move forward in the reservoir at equal rates.

The well completion technique described above in relation to FIGS. 1 through 6 is especially useful in the injection of two immiscible uids such as oil and water. To obtain maximum eflciency of the driving iluid the mobility ratio of the driving fluid should be controlled. It is normally desired that the mobility ratio be one. The mobility ratio is expressed in the following manner:

K0 Fw ml-KWX llo wherein m1 is equal to the mobility index, Ko is the permeability of the reservoir rock to oil, KW is the permeability of the reservoir rock to water, uw is the viscosity of the water and ,uo is the viscosity of the oil. Although oil and water will be used herein for simplification of the system, it will be understood that other immiscible fluids may be used and the same formula will be applicable. The uids can be gas and liquid or any combination thereof.

Attention is now directed toward FIG. 7 which illustrates a set of curves from which the prOpcr rati() Of the two different uids can be determined to give a selected mobility index. The ordinate of the curve in FIG. 7 represents permeability. The abscissa represents the fraction of the pore volume of the reservoir rock occupied by water. There are two curves on the graph. One is labelled oil and represents the permeability of the formation to oil for various water saturations. The other curve is labelled water and represents the various permeabilities to water for different water saturations in the reservoir rock.

An example will now be given showing how to select the proper ratio of oil and water to obtain a mixture whose constituents will move through the reservoir rock at equal rate of speed; i.e. have a mobility index of one. If this system is to be used, for example, with water and oil it will be assumed that the viscosity of the oil is .1 centipoise and that of the water is .9 centipoise. Then uw/p0 equals 9. If m1 is to equal 1 then K/KW must equal l/9. This is represented on the graph by x/ y. In other words, a point is selected on the abscissa such that the permeability, at that point, of the oil divided by the permeability, at that point, of the water is equal to l/ 9. The percent water saturation at which y/ x equals jaw/,un is the percent water which is to be used to obtain a mobility index of one. In the example illustrated the percent of water saturation is Expressed differently, there will be 4 volumemswofminjected watevrqfvomrhf.,aclg` injected volume of oil. As explaiiidmbive' and according to this invention, the water will be injected through one channel from the surface to within the formation; and the oil will be injected through a second channel to within the formation. rlihe mixture thus injected will move through the reservoir as a unit if the mobility index of one is maintained.

In actual practice, the two curves illustrated may not be able to be defined absolutely. To overcome this deciency, the ratio of oil to water should be gradually varied back and forth across the optimum calculated value. As, for example, if the optimum ratio of oil to water is 1 to 4, the ratio should be varied about i5% of this value.

While there are above disclosed but a limited number of embodiments of the structure and system of the iniention herein presented, it is possible to produce still other embodiments without departing from the inventive concept herein disclosed. It is therefore desired that only such limitations be imposed on the appending claims as are stated therein.

What is claimed is:

1. A secondary recovery system wherein two immiscible fluids having different specific gravities are injected as a driving mechanism through a well penetrating the subterranean formation in quantities to obtain the mobility index of one the improvement which comprises: injecting one of said fluids into said formation through one portion of the well; simultaneously injecting the other of said fluids into said formation from another portion of the well so that the two fluids form a mixture within 'the formation; varying the ratio of one fluid with respect vto the other in a range from about -l-5% to about 5% of the ratio of one uid to the other required to maintain a mobility index of one.

2. In a secondary recovery system wherein two immiscible fluids having different specific gravities are injected as the driving means through an input well perforating a subterranean formation the improvement which comprises: establishing twogeparatgchannels.with; in Saidw1 1. fr9ta-the surface ,to .wirhinmsfcudromanos;W

siniiltaneously injecting one fluid through one channel and the other fluid through the other channel such that the IWC. lilldSiQmarnixturehvithinmtheformation; the- .2' tion through a rst portion of the well; simultaneously injecting the other of said uids into said formation from a separate portion of the Well, said portions being lo- ,cated between substantially the same vertical elevations Within the formation so that the two fluids form a mixture Within the formation; and varying the ratio of one fluid with respect to the other in a range from about l-}5% to about 5% of the ratio of one uid to the other to maintain a mobility index of l.

References Cited by the Examiner UNITED STATES PATENTS Russell 166--9 Rzasa et al. 166-9 Hall et al. 166-9 Martin 166-9 Slobod 166-9 Henslee 166-243 Baker et al. 166-243 Gaskell et al 166-9 CHARLES E. OCONNELL, Primary Examiner. BENJAMIN BENDETT, NORMAN YUDKOFF,

Examiners. 

1. A SECONDARY RECOVERY SYSTEM WHEREIN TWO IMMISCIBLE FLUIDS HAVING DIFFERENT SPECIFIC GRAVITIES ARE INJECTED AS A DRIVING MECHANISM THROUGH A WELL PENETRATING THE SUBTERANEAN FORMATION IN QUANTITIES TO OBTAIN THE MOBILITY INDEX OF ONE THE IMPROVEMENT WHICH COMPRISES: INJECTING ONE OF SAID FLUIDS INTO SAID FORMATION THROUGH ONE PORTION OF THE WELL; SIMULTANEOUSLY INJECTING THE OTHER OF SAID FLUIDS INTO SAID FORMATION FROM ANOTHER PORTION OF THE WELL SO THAT THE TWO FLUIDS FORM A MIXTURE WITHIN THE FORMATION; VARYING THE RATIO OF ONE FLUID WITH RESPECT TO THE OTHER IN A RANGE FROM ABOUT +5% TO ABOUT -5% OF THE RATIO OF ONE FLUID TO THE OTHER REQUIRED TO MAINTAIN A MOBILITY INDEX OF ONE. 